Prices for all of the major chains started to slip yesterday, and are way down today with AMC, Regal Entertainment, Imax, and cinema ad sales company National CineMedia touching 52-week lows.

Over the last two days AMC’s stock price fell 10.2% (including 6.5% in mid-afternoon trading today), National CineMedia is -9.8% (-4.1% today), Imax is -4.1% (-0.6% today), Regal is -3.8% (-2.6% today), and Cinemark is -2.8% (-2.5% today).

The overall market, measured by the Standard & Poors’ 500, was -1.2% as investors grow increasingly concerned that U.S. and North Korea might act on escalating threats to engage in military actions.

Several analysts were at a loss to identify a catalyst for the steep drops for exhibitors.

Yesterday research firm IHS Markit noted that short sellers recently “materially increased their positions” in exhibition chains. Short sellers bet that a company’s stock price will fall; they borrow shares and then sell them hoping they can buy them back at a lower price before they have to return them to the original owner.

Short sellers control about 24.7% of Regal’s float — or shares issued to the public — according to Yahoo Finance. That’s followed by AMC with nearly 19.0%, Imax with 12.5%, Cinemark with 8.1%, and National CineMedia with 5.2%.

Wall Street began to sour on exhibition in the spring. Many were turned off by disappointing U.S. box office sales, which in Q2 fell 4.4% vs the period last year. Hollywood studios added to those concerns by talking up their hope to introduce premium video on demand (PVOD) — giving home viewers an opportunity to watch releases within the first 90 days when theaters typically offer them exclusively.

Netflix also said it was ramping up its production of feature films which it will introduce simultaneously online and in theaters.

Early last week AMC seemed to pour gasoline on the embers of fear by unexpectedly pre-announcing Q2 earnings that fell far short of Wall Street expectations. It added that it anticipates “a very challenging” Q3 and predicted that industrywide North American box office sales will come in at $11.2 billion — down 1.8% vs last year.

The next day, AMC lost about a quarter of its market value.

Aron seemed to ease many investors’ concerns on Friday when he spent two hours answering analysts’ questions. He said that although he’s “extremely disappointed” in AMC’s Q2 performance, it’s “well positioned for the future.”

He talked up Q4 releases, including Star Wars: The Last Jedi. And he said that his conversations with studio chiefs persuaded him that they would not try to introduce PVOD this year, in part because there’s no consensus over terms.

The company, owned by China’s Dalian Wanda Group, sought to demonstrate its optimism by approving a plan to repurchase $100 million of AMC’s publicly traded shares over the next two years. Aron underscored that by saying he plans to personally buy an unspecified amount of AMC shares over the next 60 days.